Modern furniture for sitting or lying upon can be equipped with electric positioning drives. An electric circuit for controlling the drives is, for example, described in generic European patent specification EP 0615667 B2. Using the arrangement disclosed there for isolating the supply current from control devices, isolation from the mains can be achieved, with simple technical means and without additional, manual switching operations, during those times at which no control functions are to be performed.
In the indicated prior-art arrangement for isolating the supply current, the operating voltage is applied to a servomotor via a relay, where the relay coil is connected to the operating potential via a push-button switch displaying a single switching contact. In addition, a further relay is provided, which is located in the mains lead to the transformer and is also actuated via the push-button switch indicated. This push-button switch is usually located on a hand-held control element, which is connected to the other elements of the electric circuitry arrangement via a cable. However, if a fault, such as a short-circuit, occurs in the cable or the push-button switch, for example, this can result in unwanted control functions being triggered. It is possible in such cases, for example, that servomotors are actuated without the user having operated the corresponding push-button switch. As a result, operating situations are possible that can also involve a certain hazard potential.